Lens Spotlight
HLB M Plan Apo 7x
The HLB Plan Apo 7x is a microscope objective designed for metallurgical applications. This test aims to evaluate how well it performs in focus stacking setups without the use of a professional microscope.
The Objective
The HLB M Plan Apo 7x was developed for metallurgical applications and is part of a parfocal objective series featuring different magnifications but identical overall length (housing plus working distance). The housing diameter also remains nearly constant—a significant design challenge, especially at lower magnification levels.
The benefit of this parfocality is particularly evident in specialized microscopes with fixed camera extension and built-in tube lenses, but it also proves useful in focus stacking setups, where lenses can be swapped without any mechanical adjustments.
Designed as a reflected-light objective, the HLB M Plan Apo 7x offers better color reproduction than many transmitted-light microscope objectives. Its long working distance—which is essential in metallurgical work, where lighting is often applied from the side—also makes illumination much easier in photography. This makes the lens a practical option for high-quality macro imaging with full-frame sensors.
The HLB Plan Apo 7x is part of a parfocal objective series with a uniform housing diameter.
The Manufacturer
The HLB M Plan Apo is manufactured by the Japanese company Shibuya Optical, which specializes in lenses, specialized microscopes, and optical accessories for a wide range of professional fields. Distribution in Europe is handled by Stonemaster (www.stonemaster.de).
The parfocal objective series from Mitutoyo, known for its long working distance and excellent imaging performance, is considered the design benchmark—though it comes at a significantly higher price point. The HLB objectives are positioned as more affordable alternatives and, in some cases, offer comparable optical quality. In addition, numerous Chinese clones exist that closely mimic the Mitutoyo design in appearance, but generally fall short in image performance.
The lens featured here was kindly provided for testing by Rainer Ernst of Stonemaster.
Technical Specifications
Magnification: 7x
Numerical Aperture: 0.22
Infinity-corrected optics (requires tube lens)
Compatible tube lens focal length: 200 mm
Thread diameter and pitch: M26 x 0.706
Weight: 245 g
Housing length: 58.6 mm
Housing diameter: 34 mm
Parfocal distance (housing length plus working distance): 95 mm
Focal length: 28.6 mm
Working distance: 36.4 mm
Resolution: 1.25 µm
Depth of field: 5.7 µm
Imaging Performance – 208 mm Tube Lens
The following test images illustrate the optical performance of the lens. The first shows an overview shot (full-frame sensor) using the Raynox DCR 150 tube lens, resulting in an approximate nominal magnification of 7x. The two subsequent images each show a magnified crop.
Test image at nominal magnification (DCR 150), with frame markers for the following cropped enlargements – good sharpness, no visible corner darkening, free from chromatic aberrations, and minimal edge distortion.
In the central cropped enlargement, good and consistent detail sharpness, free from chromatic aberrations.
In the corner cropped enlargement, the decrease in detail sharpness is clearly noticeable, though still quite moderate. A slight pincushion distortion is also visible in the corners, but it would hardly be noticeable without upscaling.
Die folgenden Testbilder veranschaulichen die optische Leistung des Objektivs. Das erste zeigt eine Übersichtsaufnahme (Vollformatsensor) mit der Tubuslinse Raynox DCR 150, was zu einer annähernden Nominalvergrößerung von 7x führt. Die beiden nachfolgenden Bilder zeigen jeweils einen vergrößerten Ausschnitt.
The image quality of the HLB Plan Apo 7x in this capture is consistently impressive—particularly considering the relatively high NA for an industrial lens and the use of a full-frame sensor, which tends to push the image circle to its limits.
Center
At the image center, the lens delivers excellent detail reproduction, crisp line rendering, and stable microcontrast. The fine structures of the test chip—narrow circuit traces, rectangular contact pads, and text markings—appear clearly separated and sharply defined. Transitions between light and dark areas are well-resolved, with no visible blooming or contrast softness. The optical precision shown here is fully in line with what one would expect from a numerical aperture of 0.22.
Extended Center
In the extended center region, this quality remains impressively consistent. Edges still appear sharp, and resolving power stays high. Features such as tapering circuit paths and microscopically fine divisions retain their differentiation, with only a minimal loss of microcontrast. The drop in sharpness is so subtle that it would only be noticeable in extremely critical subjects or under close comparative inspection.
Edge Zone
Only in the outer edge zone—particularly at the extreme edges of the image field—do the expected limitations of using a full-frame sensor become apparent. Lines begin to soften slightly, and there's a mild flattening of fine details. However, chromatic aberrations and distortion are not significantly present—evidence of the lens’s good optical correction. Notably, even in the edge zone, there is no disturbing color shift, and structural rendering does not collapse—it simply diminishes slightly. The edge falloff remains moderate overall.
Overall Impression
The HLB Plan Apo 7x delivers impressive sharpness in the center and extended center areas on a full-frame sensor, along with a generally respectable edge performance. The lens is well-suited for high-precision macro photography focused on centrally placed subjects—particularly in technical and scientific contexts. Considering its price-to-performance ratio, the optical quality is high and, with proper setup, approaches that of professional-grade optics.
What’s especially noteworthy is how well the lens appears to pair with the tube lens used (208 mm, which is very close to the ideal 200 mm). Under these conditions, the optical performance seems to be fully realized, with no significant loss in quality due to an unsuitable system configuration.
Imaging Performance – 125 mm Tube Lens
The following test image is another overview shot, this time taken with the Raynox DCR 250 tube lens, which reduces the magnification to approximately 4.375x (instead of 7x). Some metallurgical microscope objectives from the mentioned HLB series tolerate this approach to varying degrees, and the test aims to evaluate what qualitative compromises can be expected when using the Mitutoyo M Plan Apo 7x under these conditions.
Test image with DCR 250: This shorter tube lens focal length results in a lower magnification, and in this combination, noticeable darkening is visible along the edges—especially in the corners.
In the central cropped enlargement, detail sharpness is higher in the center than in the corners. This indicates that the shorter tube lens focal length causes the lens’s aberration-prone outer zones to be utilized.
In the corner cropped enlargement, distortion and blurriness increase dramatically toward the edge.
When using a tube lens with only 125 mm focal length, the test image captured with the HLB Plan Apo 7x clearly demonstrates how sensitive this objective is to deviations from its intended optical configuration. An analysis of the image field reveals that even the center suffers from a noticeable loss of sharpness and contrast.
Center
In the center, the circuit patterns of the test target are still discernible, but fine line rendering begins to blur. Edges appear slightly softened, microcontrast is reduced, and transitions between light and dark areas lack precision. The resolution of small structural elements falls short of what this objective can achieve when used with the correct 200 mm tube lens.
Extended Center
In the extended center, these deficiencies become more pronounced: lines visibly merge, structures start to blur, and the image takes on a noticeably hazy appearance—often associated with spherical aberrations or field curvature when the optical correction is not operating within its designed light path.
Edge Zone
In the edge zone, image quality breaks down significantly. Resolution drops considerably, dark areas lose detail, highlights are slightly overblown, and the geometric structure of the test image becomes less defined. The edges appear diffuse, with sloppy transitions and an overall loss of image information—a combination of blurring, aberrations, and likely field curvature, caused by the strong deviation from the calculated optical path.
Another likely reason for the quality loss when using a shorter tube lens is the effective reduction in magnification to around 4.4x instead of the intended 7x. This not only changes the image size but also alters the relationship between aperture and light path, which in turn affects the effective numerical aperture and overall image performance—particularly when paired with a large sensor such as full-frame.
Overall Impression
The HLB Plan Apo 7x is clearly optimized for use with a 200 mm tube lens (or an equivalent setup, such as the DCR150 with a 208 mm extension). When used with a tube lens of only 125 mm focal length, the optical performance deteriorates across the entire image field—starting at the center, increasing in the extended center, and becoming severe at the edges. This configuration is not recommended for serious applications. To fully exploit this objective’s capabilities, it is essential to use a properly matched tube lens.
Comparison HLB M Plan Apo 7x und Mitutoyo M Plan Apo 7,5x
The direct comparison with the Mitutoyo M Plan Apo 7.5x shows that the HLB M Plan Apo 7x is very much on par with this extremely high-quality, sharp-rendering objective—at least when used with a tube lens focal length of around 200 mm.
The HLB M Plan Apo 7x demonstrates its capabilities in comparison with the Mitutoyo M Plan Apo 7.5x, and both are shown side by side in the direct comparison below.
HLB M Plan Apo 7x
The HLB delivers very good resolution in the center: fine circuit traces are clearly separated, contrast levels are sharply defined, and micro-contrast is well preserved. This quality remains nearly unchanged in the extended center—an indication that the optics harmonize well with the image circle of a full-frame sensor. Only toward the edges does the rendering become slightly softer, but not to a disturbing extent. The image remains clearly structured even in the corners and is free of color fringes or astigmatism. A slight reduction in micro-contrast is noticeable, but it is well within acceptable limits given the sensor size and NA performance.
Mitutoyo M Plan Apo 7.5x
The Mitutoyo lens also exhibits excellent imaging performance—perhaps even a touch finer in the center, particularly in the most intricate structures (such as the fine branches in the upper left corner of each chip). The lines appear just a bit more precisely separated, the micro-contrast is marginally higher, and the grayscale gradations show slightly better differentiation. In the extended center and even out to the edges, the image quality remains at a very high level—the image appears completely cohesive, with virtually no visible chromatic or geometric aberrations.
Impression
Overall, the Mitutoyo M Plan Apo 7.5x delivers marginally better detail separation and a slightly more balanced contrast profile. However, the HLB lens impresses with an almost equivalent optical performance—differences only become apparent in a direct side-by-side comparison. Most notable is the fact that the HLB achieves this level of performance at a typically much lower price. Those seeking absolute optical perfection will likely choose the Mitutoyo. But for anyone looking for an excellent 7x objective with high sharpness, long working distance, and outstanding value for money, the HLB presents a serious alternative—surprisingly close to the reference class.
Imaging Performance – 208 mm Tube Lens: Microprocessor
A tiny microprocessor designed for use in mobile phone electronics features extremely delicate structures. Measuring just 3 x 3 mm, the image of this chip illustrates not only the resolving power and detail rendition of a lens, but also its color reproduction capabilities.
Crisp, sharp rendering of delicate details, with good color contrast and only extremely slight, barely noticeable pincushion distortion in the corner areas—mainly because the overview image was heavily cropped all around due to the small magnification ratio.
The two images shown provide a compelling demonstration of the HLB Plan Apo 7x’s optical performance under optimal conditions—that is, when used with the intended tube lens focal length of approximately 200 mm (in this case, 208 mm) and a high-quality full-frame sensor. Even the overview image of the 3 × 3 mm microprocessor reveals a high level of differentiation in complex structures across the entire image field. In particular, the fine trace patterns within the central processor unit are clearly resolved, with sharply defined contrasts and well-reproduced color nuances in reflected light.
In the enlarged detail view (corresponding to the red frame in the overview), the lens’s excellent fidelity becomes even more apparent: Even the finest line structures, which are in the submicron range, are captured without noticeable artifacts or loss of resolution.
Also notable is the uniformity of color rendering: There is no distracting color banding, no chromatic aberration, and no visible field curvature. Edge sharpness in highly reflective areas—such as the silvery solder pads around the perimeter—remains clean. Overall contrast is somewhat lower than in pure transmitted-light systems, which is typical for reflective-light setups of this kind and can be easily enhanced through digital post-processing.
The HLB Plan Apo 7x fully demonstrates its strengths when configured correctly. In this shooting scenario, it performs as a high-resolution precision lens with excellent field flatness, very good microcontrast, and remarkable consistency all the way to the edges—making it ideal for demanding applications in technical macro photography and microsystem analysis.
Resolution Test
The Zeiss Resolution Test 300 allows the resolution of a microscope objective to be quantified as a numerical value. While this reading involves a degree of interpretation and is not entirely precise (see details here), it does provide a useful general impression of the lens’s fine detail rendering and overall image sharpness.
The resolution value, visible here in the two outer fields, was measured at the center of the lens at 500 line pairs per millimeter (lp/mm).
Conclusion
The HLB Plan Apo 7x is a high-performance industrial objective that, when used correctly—with the specified tube lens focal length of 200 mm—delivers image quality nearly on par with the renowned Mitutoyo M Plan Apo 7.5x. Sharpness, detail resolution, and field flatness are impressive, particularly in the center and extended center, and remain remarkably consistent even into the edges of a full-frame sensor without any major compromises. Its numerical aperture of 0.22 contributes to well-defined fine structures and strong microcontrast.
However, the HLB 7x shows significantly less tolerance for deviations from the ideal optical configuration than its Mitutoyo counterpart. When used with a reduced tube lens focal length (e.g., 125 mm), image quality noticeably declines—especially in the periphery. In contrast, the Mitutoyo 7.5x proves far more resilient in this regard and maintains strong performance even under suboptimal conditions.
Thus, for users working with a precisely configured setup and aiming to extract maximum performance from a precision lens, the HLB 7x presents a serious, high-quality alternative to the Mitutoyo—at a significantly lower price point. For those requiring more flexibility with varying setups or tube lenses, however, the Mitutoyo remains the more robust, albeit more expensive, all-rounder.
Advantages
Extremely long working distance, high image sharpness and detail accuracy, parfocality within the objective series allowing for easy lens changes, and a price advantage compared to the Mitutoyo reference objective.
Disadvantages
Unusual thread size requiring a special adapter (e.g., www.stonemaster-onlineshop.de); significant loss of image quality when using a shorter tube lens focal length (DCR 250).
Daniel Knop, www.knop.de, www.danielknop.eu
Testbild mit DCR 250: Im Zentrum ist die Bildschärfe bei dieser Kombination nur moderat und deutlich geringer als bei der Nominalvergrößerung, und außerhalb des Bildzentrums lässt sie gewaltig nach. Hier zeigt sich auch eine leichte kissenförmige Verzerrung. Die Abdunklung des Rand- und Eckenbereichs ist deutlicher als bei Verwendung der DCR 150.
Das Bildzentrum hat noch gewisse Schärfe, aber feinste Details werden in Kombination mit der DCR 250 nicht mehr wiedergegeben.
Die Randzone weist starke kissenförmige Verzerrung und intolerable Unschärfe auf, die zur Ecke hin extrem wird (hier links oben). Im Vollformat ist diese Kombination aus Objektiv und Tubuslinse schlicht unbrauchbar.
Der direkte Vergleich mit dem Canon-Lupenobjektiv MP-E 65 mm bei Stellung 3,5x zeigt, dass das HLB Planapo 3,5x diesem sehr scharf abbildenden Makrospezialisten deutlich unterlegen ist. Das Canon bringt mehr Schärfe (Bild oben rechts), und der Schärfeabfall zum Bildrand und vor allem zu den Ecken hin ist beim Canon deutlich schwächer als beim HLB. Allerdings muss hier auch berücksichtigt werden, dass das HLB Planapo 3,5x neu weniger als die Hälfte dessen kostet, was für ein Canon MP-E 65 mm zu veranschlagen ist.
Vergleich HLB M Plan 3,5x – Canon MP-E 65 mm
HLB Planapo 3,5x (links) im Vergleich mit dem Canon MP-E 65 mm bei Stellung 3,5 (rechts), oben jeweils das rechte obere Viertel des Originalbilds, aufgenommen mit Vollformatsensor (Focus Stack), unten jeweils ein Sechzehntel des Originalbilds, entsprechend hochskaliert.
Fazit